This invention relates generally to an electric heating device and more particularly to such a device having improved control of energization.
In an automobile, gasoline is atomized and, if necessary, a suitable amount of air is automatically supplied, thereby obtaining a combustible gas (mixed gas), which is then supplied to the combustion chamber of the engine. A carburetor is employed for obtaining a mixed gas of air and gasoline.
This may be explained with reference to FIG. 6. A throttle body 21 is formed as a venturi tube whose intermediate range diameter is reduced. Due to air 22 that has been supplied through a butterfly valve 27 from this air supply opening, the gasoline 24 inside the float chamber 23 is atomized at the tip of a nozzle 25. A mixed gas 26 of this atomized gasoline and air is preliminarily heated by a honeycomb heater 29 through a butterfly valve 28 and is led to the combustion chamber of the engine (the combustion chamber is not shown in the drawings) through a branching pipe of an intake manifold 30.
It is mentioned in this connection that the throttle body 21 and the intake manifold are, in effect, integral with each other having an air tight connection therebetween, with a gasket 32 serving as an insulator that surrounds the honeycomb heater 29. A large number of gas passageways 38 are formed in a dense array on the honeycomb heater 29 and, as the heater itself is made electrically conductive, the mixed gas that passes therethrough is heated to a prescribed temperature, thereby effecting the prevention of knocking and the economy of the fuel that is consumed.
In the manifold 30, there is formed a warm water passageway 33 that directs water that has been warmed as it passes the cold water jacket around the cylinder liner that is not shown in the drawings. The honeycomb heater 29 is so constructed that electric power is de-energized when the temperature of the engine cooling water rises to a selected value (such as 70 degrees centigrade, to cite an example) for the purpose of saving electricity on the part of the battery 39.
FIG. 7 is a schematic diagram of an electric circuit designed for use with the honeycomb heater 29. A water temperature sensor 34 that detects the temperature of the engine cooling water is provided in the cooling water passageway and a signal that operationally controls a magnetic switch 36 is outputted from a control unit 35 on the basis of the water temperature detected.
Accordingly, in the case where the water temperature has exceeded a standard value, the switch 36 turns off, with a result that the electric current flow to the honeycomb heater 29 is terminated. Numeral 37 in the figure indicates an ignition switch.
According to the manifold heating method using warm water as described above, the warm water that has been employed as cooling water does not necessarily maintain a constant temperature at all times but changes in accordance with operation conditions of the engine or different loads. The use of warm water accompanying such temperature changes as a heat source results in frequent energization and de-energization of the honeycomb heater. This is undesirable since it results in excessive use of the electric circuit system shown in FIG. 7.
According to the method of heating the manifold by warm water, further, it is necessary to provide a complicated electric circuitry system for control such as water temperature sensor 34 and control unit 35 for effecting the aforementioned control of the honeycomb heater 29. This is generally disadvantageous in terms of mounting operations.
The aforementioned problem exists not only in an automobile engine but also in the heating parts of various machines and apparatus.